Kuja is narcissistic in contrast to Zidane's humility. Kuja has an ego to match his power, and he lets his pride rule his head. Kuja once chose to let Zidane live even if he had a chance to kill him to prove himself superior. After discovering his destiny as a mortal, Kuja's cultured personality turns into insanity, believing life should not be allowed to continue without him. His descent into insanity and rebellion against Garland stem from the fear of oblivion, as Garland intended to discard Kuja's soul in favor of a new Genome. He is unfazed by being wounded, shown when being attacked by Bahamut.

Kuja uses his elegance to hide his insecurities, and deep down is conflicted over his existence. Kuja scorns the black mages he helped create, but also finds himself identifying with them. As explained in Final Fantasy IX Ultimania, Kuja never experienced childhood, and thus his emotional growth is stunted and he cannot use Trance. Kuja is initially unable to empathize with others or feel remorse for his actions. It appears that learning of his fate as a mortal and rebelling against this destiny allows Kuja to grow, as after losing his fight he comes to see at least some of the repercussions of his actions and to regret them. He acts kindly toward Zidane in their short exchange at the Iifa Tree, glad that Zidane's friends were able to escape.